docs: def validate_unset_command(self, line: str, position: int, annotation: str) -> None:
          """Raise an exception when trying to ``UNSET X`` if ``X`` is not already set.
  
          :raises: MissingAnnotationKeyWarning
          """
          if annotation not in self.annotations:
              raise MissingAnnotationKeyWarning(self.get_line_number(), line, position, annotation)